The purpose of this research is to provide information on the mode of action of nerve growth factor. Nerve growth factor is required for the development and maintenance of the sympathetic nervous system and may be prototypic for factors involved in differentiation of various cell types. The mechanism by which nerve growth factor induces the enzymes involved in the synthesis of the sympathetic transmitter, norepinephrine, must be understood to permit a full understanding of the mechanism. Finally, nerve growth factor action must be understood before complete information is available about the development and differentiation of the non-dividing, non-replaceable neurons of the central nervous system.